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St. Louis encephalitis is one of the most common human diseases caused by infected mosquitoes in the United States.
Between 1964 and 2005 (the most recent data available), about 4,650 confirmed cases of St. Louis encephalitis were reported, with a peak of almost 2000 cases in 1975, according to the Centers for Disease Control and Prevention (CDC). Many more cases are believed to go undiagnosed.
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Symptoms requiring emergency care include:
- Sudden stiff neck combined with high fever or other signs of illness.
- Convulsions (call 911).
Seek medical attention if you have a high fever.
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St. Louis encephalitis is one of several mosquito-borne viral diseases that can affect the central nervous system and cause severe complications and death. St. Louis encephalitis and other similar diseases, such as eastern equine encephalitis, western equine encephalitis and Japanese encephalitis, are all caused by arboviruses. Arbovirus is short for arthropod-borne virus.
In the United States, arboviruses usually are spread from of a bite of a mosquito, which very often becomes infected by feeding on infected birds. Even though an arbovirus such as St. Louis encephalitis grows in an infected mosquito and infected bird, it does not make either one sick.
What's more, people cannot get the disease directly from birds or from insects other than mosquitoes, nor can they get it from another person who has the disease.
St. Louis encephalitis is found throughout North America, Central America, South America and the Caribbean but is a major public health problem mainly in the United States.
St. Louis encephalitis was first isolated in 1933 during an epidemic in St. Louis, Missouri and during the years has continued to cause epidemics in other parts of the country. The last major epidemic infected about 2,000 people throughout the Mississippi Valley in 1975.
The largest outbreaks in the last 20 years occurred in 1990 in Florida and Texas. According to the CDC, the risk of exposure is increasing in urban areas as deteriorating inner cities create habitats for mosquitoes.
Anyone can get the disease, but some people who are at increased risk of getting the disease include the elderly, people who live in crowded, low-income areas and people who work outside or participate in outdoor recreational activities in an area where the disease is common.
This article was reviewed and updated June 2007.
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